Synthesis of responsive polymer tethered nanoparticles and graphene oxides for their application in optical sensors

Abstract

Highly-sensitive and selective detection methods have become an increasing interest in the investigation of environmental, analytical chemistry, and biomedical applications. Particularly, optical sensors based nanoparticles offer many advantages over conventional electrochemical approaches, including high sensitivity and easily detected by naked eye. Stimuli-responsive polymers are smart materials that exhibit reversible changes in their chain conformation in response to external stimuli. F"orster resonance energy transfer (FRET) is a mechanism describing energy transfer between two chromophores. A donor chromophore, initially in its electronic excited state, may transfer energy to an acceptor chromophore through nonradiative dipole-dipole coupling. Particularly, the efficiency of this energy transfer is inversely proportional to the sixth power of the distance between donor and acceptor making FRET extremely sensitive to small distances. Thus, the integration of stimuli-responsive polymers with fluorescent materials can produce optically active smart materials. In this thesis, we developed a simple and robust route for the fabrication of a ratiometric optical sensor, based on responsive-polymer tethered quantum dots (QDs) and graphene oxide. FRET between two distinguish-able chromophores is governed by the interspacing between them, which can be controlled through manipulation of the conformational features of the responsive polymer chains that respond to external stimuli. First, fluorescent and pH-responsive poly((1-pyrene)methyl-2-methyl-2-propenoate))-b-poly(2-vinylpyridine) (PyMMP-b-P2VP) block copolymers were designed and synthesized on the CdSe/ZnS QDs using the facile “grafting-from” method with RAFT polymerization. The P2VP chains change their chain conformation around pH 3, and subsequently facilitating the FRET from the PyMMP to the QDs and causing the observed color change from blue to red. While responsive polymer exhibit interesting chain confor...